The present invention relates to theft detection systems and particularly those for use in vehicles.
Automotive vehicles are an important aspect of life in modern society. Beyond simply providing a means of transportation, vehicles today also provide consumers with a variety of optional features to maximize convenience, comfort, and safety. The trend towards accesorization, however, has caused automotive vehicles to become more expensive and thus more valuable. As an unfortunate result, the threat of automotive theft has become an increasingly important concern.
A multitude of alarm systems have been designed to prevent or deter the theft of automobile vehicles. The operation of many of these systems is dependent upon the detection of activity which is likely to be attributable to vehicle theft. One method of theft detection involves sensing unauthorized movement of a vehicle and is especially useful for preventing vehicle theft accomplished by towing the vehicle or placing it on a flat-bed track. Alarm systems usually employ sensors which are dependent upon the motion of the vehicle causing mechanical movement of internal sensor elements. One type of sensor senses vehicle motion by monitoring an internal sensor variable, such as magnetic flux, inductance, or induced voltage, which changes due to movement of an internal movable sensor element such as a magnet or a drop of mercury. Mother type of sensor senses vehicle motion by monitoring an internal sensor variable, such as capacitance or resistance, which changes due to movement of special fluids within the sensor.
Although these prior art systems provide a measure of protection against vehicle theft, their dependency on the motion of the vehicle causing movement of internal sensor elements may result in the non-detection of vehicle motion in some circumstances. In particular, these systems may have difficulty sensing vehicle theft when the vehicle is initially parked on an incline because the position of the vehicle may prevent proper motion of the internal sensor elements. Furthermore, the mechanical nature of the sensors of most of these prior art theft detection systems increases the cost of the systems and can reduce their reliability. Also, the sensors of these systems are application specific such that they cannot be used to provide functions in addition to theft detection.
Thus, a need exists for a theft detection system designed to detect vehicle motion without dependency upon the mechanical movement of internal system elements such that vehicle theft can be detected in all situations and that the expense of the system is minimized and its reliability improved. Furthermore, a theft detection system having a sensor that is useful in applications in addition to theft detection would be preferred.